1. Field of the Invention
The present invention relates to a computer keyswitch, and more particularly, to a computer keyswitch with accurately positioned rubber domes.
2. Description of the Prior Art
A computer keyswitch is a common input device. It comprises a base plate, a membrane circuit board installed on the base plate having a plurality of pressure sensors, a plurality of upwardly protruding rubber domes each on a pressure sensor of the membrane circuit board, and a plurality of keycaps each on a rubber dome. Each of the rubber domes is used to elastically support a corresponding keycap. When the keycap is depressed, the rubber dome will trigger the pressure sensor underneath to generate a key-pressing signal. There are two types of rubber domes. Rubber domes of the first type are monolithically formed on a rubber sheet. These rubber domes are automatically positioned on corresponding pressure sensors when the rubber sheet is placed on the membrane circuit board. Rubber domes of the second type are of a stand-alone type. They are individually positioned on the pressure sensors of the membrane circuit board. Nowadays, research is focused on reducing the thickness and weight of the keyswitch. Moreover, means for improving the positioning precision of the rubber domes on the pressure sensors is also strongly considered.
Please refer to FIGS. 1 and 2. FIG. 1 is a component diagram of a keyswitch 13 of a computer keyswitch. FIG. 2 is a cross-sectional view of the keyswitch 13. The keyswitch comprises a base plate 12, a membrane circuit board 14 installed on the base plate 12, and a rubber sheet 20 positioned on the membrane circuit board 14. The rubber sheet 20 has a plurality of upwardly protruding rubber domes 22 on its upper side 23, and three penetrating holes 31 set up around each of the rubber domes 22. The membrane circuit board 14 has a plurality of pressure sensors 16 for generating key-pressing signals and three penetrating holes 30 installed around each of the pressure sensors 16. The base plate 12 has a plurality of holding legs 32 protruding upwardly through the penetrating holes 30, 31 on the membrane circuit board 14 and the rubber sheet 20. In order to reduce the thickness of the computer keyswitch, the thickness of the rubber sheet is often reduced, causing a weakened structure of straps 21 around each rubber dome 22 and thus distortions of the straps 21. This will then generate position errors between the rubber domes 22 and the pressure sensors 16.
Please refer to FIGS. 3 and 4. FIG. 3 is a component diagram of a keyswitch 37 of another computer keyswitch. FIG. 4 is a cross-sectional view of the keyswitch 37. The computer keyswitch comprises a base plate 11, a membrane circuit board 17 installed on the base plate 11, a plurality of stand-alone rubber domes 23 installed on the membrane circuit board 17, and a plastic frame board 34 installed on the membrane circuit board 17 for fixing positions of the rubber domes 23. The membrane circuit board 17 has a plurality of pressure sensors 16 for generating key-pressing signals. The plastic frame board 34 has a plurality of penetrating holes 35 positioned corresponding to the pressure sensors 16. When the plastic frame board 34 is installed on the membrane circuit board 17, the rubber domes 23 on the pressure sensors 16 will penetrate through the penetrating holes 35 of the plastic frame board 34, and edges 23a of the rubber domes 23 will be clamped between the plastic frame board 34 and the membrane circuit board 17. Using the plastic frame board 34 to fix the positions of the rubber domes 23 has the drawback of increasing the thickness of the computer keyswitch.